The present invention relates to longwall mining machines, particularly to such machines for working thin seams, in which one or more drive motors are connected through a gear train on one side of the machine to two cutting drums at opposite ends of the machine. The machine is moved along a guide track by a gear wheel which meshes with a rack formed along the track, the rack and gear wheel usually being on the side of the machine opposite the aforesaid gear train.
In the past, longwall mining machines of this type have been provided in which a gear train on one side of the machine drives cutter drums carried on pivotal support arms at opposite ends of the machine. It is also known in the prior art to provide electrical clutches having a direct current energized magnet wheel rotatably mounted in a casing and having a winding around it. The magnet wheel extends around an armature which is disposed on a shaft and is arranged centrally within the magnet wheel. In the event of speed differences between the outer magnet wheel and the inner armature, usually a squirrel-cage armature, the constantly energized magnet wheel has the same effect on the armature as the rotating field of an asynchronous motor. The eddy currents induced in the armature produce in the stationary or slowly rotating armature a driving torque related to excitation and to the slip speed.
Longwall mining machines, even those for working thin seams, are usually provided with self-contained means for moving the machine along its guide track. A self-contained prime mover of this type improves the controllability and maneuverability of the longwall mining machine and has the further substantial advantage of obviating the need for a chain or the like required to transmit pull from a winch which is not carried on the machine itself but rather is disposed at the end of the face being mined. A chain and external winch arrangement is a constant risk to miners working around the machine, hampers access to the face area and does not transmit the pull of the winch at one end of the face area smoothly and continuously to the mining machine. On the other hand, a self-contained driving means in the body of the mining machine takes additional space and increases the overall length of the machine. In this respect, longwall mining machines of substantial overall length are difficult to use in thin, undulating seams since adaptation of the machine body to the seam worsens as the overall length of the machine increases.